Chapter 8 Jovian Planet Systems

Key Questions…. How do we know what we do? What value is there to ask these questions, and build probes to answer them?

8.1 A Different Kind of Planet Our goals for learning: What are jovian planets made of? What are jovian planets made of? What are jovian planets like on the inside? What are jovian planets like on the inside? What is the weather like on jovian planets? What is the weather like on jovian planets?

The Jovian Planets

Jovian Planet Composition Jupiter and Saturn Jupiter and Saturn — Mostly H and He gas — Rock/Metal core Uranus and Neptune Uranus and Neptune — Mostly hydrogen compounds: water (H 2 O), methane (CH 4 ), ammonia (NH 3 ) — Some H, He — Rock/Metal core

Jovian Planet Formation Recall the CONDENSATION SEQUENCE theory: Where the planets formed dictated what solid materials they could form from. Where the planets formed dictated what solid materials they could form from. Beyond the, planetesimals could accumulate Hydrogen-rich ICE. Beyond the frost line, planetesimals could accumulate Hydrogen-rich ICE. Hydrogen compounds are more abundant than rock/metal => jovian planets got bigger & acquired H/He atmospheres. Hydrogen compounds are more abundant than rock/metal => jovian planets got bigger & acquired H/He atmospheres.

Jovian Planet Formation Jovian planet cores should be very similar: Jovian planet cores should be very similar: ~ mass of 10 Earths ~ mass of 10 Earths Rock, iron, heavier materials differentiated Rock, iron, heavier materials differentiated Differences are in amount of H/He gas accumulated. Differences are in amount of H/He gas accumulated. Why did that amount differ?

Differences in Jovian Planet Formation TIMING: “The Early Bird gets the worm.” TIMING: “The Early Bird gets the worm.” LOCATION (“Location, Location, Location!”) LOCATION (“Location, Location, Location!”)

Differences in Jovian Planet Formation TIMING: Planets forming earliest capture most hydrogen & helium gas. TIMING: Planets forming earliest capture most hydrogen & helium gas. Capture ceases after first solar winds blew leftover gas away. Capture ceases after first solar winds blew leftover gas away. LOCATION: Planets that forms in denser part of nebula forms their cores first. LOCATION: Planets that forms in denser part of nebula forms their cores first.

Density Differences Uranus and Neptune are denser than Saturn because they have less H/He, proportionately. Uranus and Neptune are denser than Saturn because they have less H/He, proportionately.

Density Differences But that explanation doesn’t work for Jupiter. But that explanation doesn’t work for Jupiter.

Sizes of Jovian Planets Adding mass to a jovian planet compresses the underlying gas layers. Adding mass to a jovian planet compresses the underlying gas layers.

Sizes of Jovian Planets Greater compression is why Jupiter is not much larger than Saturn even though it is three times more massive. Greater compression is why Jupiter is not much larger than Saturn even though it is three times more massive. Jovian planets with even more mass can be smaller than Jupiter. Jovian planets with even more mass can be smaller than Jupiter.

Sizes of Jovian Planets Jovian planets with even more mass can be smaller than Jupiter. Jovian planets with even more mass can be smaller than Jupiter. We see this with exoplanets already discovered! We see this with exoplanets already discovered!

What are jovian planets like on the inside?

Comparing Jovian Interiors Models suggest cores have similar composition. Models suggest cores have similar composition. Lower pressures inside Uranus and Neptune mean no metallic hydrogen. Lower pressures inside Uranus and Neptune mean no metallic hydrogen.

Inside Jupiter & Saturn High pressure inside of Jupiter/Saturn causes hydrogen to change its properties with depth. High pressure inside of Jupiter/Saturn causes hydrogen to change its properties with depth. Gas => => Gas => Liquid => Conducting Liquid

Inside Jupiter & Saturn Hydrogen acts like metal at great depths because its electrons move freely. Hydrogen acts like metal at great depths because its electrons move freely. Fast rotation => HUGE magnetic Field! Fast rotation => HUGE magnetic Field!

Inside Jupiter & Saturn

Jupiter’s Magnetosphere Jupiter’s strong magnetic field creates enormous magneto- sphere.

Visible Proof! Magnetic Fields channel solar wind to rotation poles Produce Aurorae Aurora on Jupiter

Visible Proof! Magnetic Fields channel solar wind to rotation poles Produce Aurorae Aurora on Jupiter

Weather on Jovian Planets All Jovian planets have strong winds & storms.

Jovian Planet Weather!

Jupiter’s Atmosphere Hydrogen compounds in Jupiter form clouds. Hydrogen compounds in Jupiter form clouds. Different cloud layers correspond to freezing points of different hydrogen compounds. Different cloud layers correspond to freezing points of different hydrogen compounds. Other jovian planets have similar cloud layers. Other jovian planets have similar cloud layers.

Jupiter’s Colors Ammonium sulfide clouds reflect red/brown. Ammonium sulfide clouds reflect red/brown. Ammonia reflects white (highest, coldest clouds) Ammonia reflects white (highest, coldest clouds)

Jupiter’s Great Red Spot A storm twice as wide as Earth A storm twice as wide as Earth Has existed for at least 3 centuries Has existed for at least 3 centuries

Saturn’s Colors Saturn’s layers are similar but are deeper in and farther from the Sun — more subdued. Saturn’s layers are similar but are deeper in and farther from the Sun — more subdued.

Belts & Zones on Saturn, too!

Storms on Saturn, too!

New Results from Cassini

Gossamer thin rings…

Saturn’s rings vary in composition, and change temperature of the planet

The longest lightening storm in history?

Methane on Uranus & Neptune Methane gas on Neptune & Uranus absorbs red light but transmits blue. Methane gas on Neptune & Uranus absorbs red light but transmits blue. Blue light reflects off methane clouds, making those planets look blue. Blue light reflects off methane clouds, making those planets look blue.

What kinds of moons orbit the jovian planets?

A Wealth of Worlds: Satellites of Ice and Rock Our goals for learning: What kinds of moons orbit the jovian planets? What kinds of moons orbit the jovian planets? Why are Jupiter’s Galilean moons geologically active? Why are Jupiter’s Galilean moons geologically active? What geological activity do we see on Titan & other moons? What geological activity do we see on Titan & other moons? Why are jovian planet moons more geologically active than small rocky planets? Why are jovian planet moons more geologically active than small rocky planets?

Sizes of Moons Small moons (< 300 km) Small moons (< 300 km) — No geological activity Medium-sized moons (300–1,500 km) Medium-sized moons (300–1,500 km) — Geological activity in past Large moons (> 1,500 km) Large moons (> 1,500 km) — Ongoing geological activity

Medium and Large Moons Spherical from gravity Spherical from gravity Substantial amounts of ice Substantial amounts of ice Formed in orbit around jovian planets Formed in orbit around jovian planets Circular orbits in same direction as planet rotation Circular orbits in same direction as planet rotation

Small Moons Far more numerous than the medium and large moons Far more numerous than the medium and large moons Not enough gravity to be spherical: “potato-shaped” Not enough gravity to be spherical: “potato-shaped”

Why are Jupiter’s Galilean moons geologically active?

Io’s Volcanic Activity Io is the most volcanically active body in the solar system, but why? Io is the most volcanically active body in the solar system, but why?

Thought Question How does Io get heated by Jupiter? How does Io get heated by Jupiter? A. Auroras B. Infrared light C. Jupiter pulls harder on one side than the other D. Volcanoes

Thought Question How does Io get heated by Jupiter? How does Io get heated by Jupiter? A. Auroras B. Infrared light C. Jupiter pulls harder on one side than the other D. Volcanoes

Io’s Volcanoes Volcanic eruptions continue to change Io’s surface

Io’s Volcanic Activity

Tidal Heating Io is squished and stretched as it orbits Jupiter. But why is its orbit so elliptical?

Orbital Resonances Every 7 days, these three moons line up. The tugs add up over time, making all three orbits elliptical.

Europa’s Ocean: Waterworld?

Tidal Stresses Crack Europa’s Surface Ice

Tidal stresses crack Europa’s surface ice Tidal flexing closes crack, grinds up ice Tidal flexing opens crack, leaving two ridges

Europa’s Interior Also Warmed by Tidal Heating

Europa’s Surface

A lava-lamp model for Europa?

Ganymede

Ganymede Largest moon in the solar system Largest moon in the solar system Clear evidence of geological activity Clear evidence of geological activity Tidal heating plus heat from radio- active decay? Tidal heating plus heat from radio- active decay?

Ganymede’s Two Faces

Callisto

Callisto “Classic” cratered iceball “Classic” cratered iceball Little/No tidal heating, no orbital resonances Little/No tidal heating, no orbital resonances But it has magnetic field !? But it has magnetic field !?

Saturn’s Largest Moon: Titan

Titan’s Atmosphere Titan is the only moon in the solar system which has a thick atmosphere. Titan is the only moon in the solar system which has a thick atmosphere. It consists mostly of nitrogen with some argon, methane, and ethane. It consists mostly of nitrogen with some argon, methane, and ethane.

Titan’s Surface Huygens probe provided a first look at Titan’s surface in early 2005 Huygens probe provided a first look at Titan’s surface in early 2005 Liquid methane, “rocks” made of ice. Liquid methane, “rocks” made of ice.

A view of Titan

Titan’s “Lakes” Radar imaging of Titan’s surface has revealed dark, smooth regions that may be lakes of liquid methane. Radar imaging of Titan’s surface has revealed dark, smooth regions that may be lakes of liquid methane.

Medium Moons of Saturn

Almost all show evidence of past volcanism and/or tectonics.

Ongoing Activity on Enceladus Fountains of ice particles and water vapor from the surface of Enceladus indicate that geological activity is ongoing. Fountains of ice particles and water vapor from the surface of Enceladus indicate that geological activity is ongoing.

Medium Moons of Uranus Varying amounts of geological activity. Varying amounts of geological activity. Moon Miranda has large tectonic features and few craters Moon Miranda has large tectonic features and few craters Hypotheses? Hypotheses?

Neptune’s Moon Triton Similar to Pluto? (but larger!) Similar to Pluto? (but larger!) Evidence for past geological activity Evidence for past geological activity

Why are jovian planet moons more geologically active than small rocky planets?

Rocky Planets vs. Icy Moons Rock melts at higher temperatures. Rock melts at higher temperatures. Ice melts at lower temperatures. Ice melts at lower temperatures.

Rocky Planets vs. Icy Moons Only large rocky planets have enough heat for activity. Only large rocky planets have enough heat for activity. Tidal heating can melt internal ice, driving activity. Tidal heating can melt internal ice, driving activity.

What are Saturn’s rings like?

Jovian Planet Rings Our goals for learning: What are Saturn’s rings like? What are Saturn’s rings like? Why do the Jovian planets have rings? Why do the Jovian planets have rings?

What are Saturn’s rings like? They are made up of numerous, tiny individual particles. They are made up of numerous, tiny individual particles. They orbit over Saturn’s equator. They orbit over Saturn’s equator. They are very thin. They are very thin. How do we know this??

Earth-Based View

Spacecraft View of Ring Gaps

Artist’s Conception of Close-Up

Gap Moons Some small moons create gaps within rings. Some small moons create gaps within rings.

Why do the jovian planets have rings?

Jovian Ring Systems All four jovian planets have ring systems. Others have smaller, darker ring particles than does Saturn.

Why do the jovian planets have rings? They formed from dust created in impacts on moons orbiting those planets. They formed from dust created in impacts on moons orbiting those planets. How do we know this?

How do we know? Rings aren’t leftover from planet formation because the particles are too small to have survived this long. Rings aren’t leftover from planet formation because the particles are too small to have survived this long. There must be a continuous replacement of tiny particles. There must be a continuous replacement of tiny particles. The most likely source is impacts with the jovian moons. The most likely source is impacts with the jovian moons.

Ring Formation Jovian planets all have rings because they possess many small moons close-in. Jovian planets all have rings because they possess many small moons close-in.

Ring Formation Impacts on these moons are random. Impacts on these moons are random. Saturn’s incredible rings may be an “accident” of our time. Saturn’s incredible rings may be an “accident” of our time.

Summary of Key Ideas

WHAT DID YOU THINK? Is Jupiter a “failed star”? Why or why not? Is Jupiter a “failed star”? Why or why not? No. Jupiter has 75 times too little mass to shine as a star. No. Jupiter has 75 times too little mass to shine as a star.

WHAT DID YOU THINK? What is Jupiter’s Great Red Spot? What is Jupiter’s Great Red Spot? The Great Red Spot is a long-lived, oval cloud circulation, similar to a hurricane on Earth. The Great Red Spot is a long-lived, oval cloud circulation, similar to a hurricane on Earth.

WHAT DID YOU THINK? Does Jupiter have continents and oceans? Does Jupiter have continents and oceans? No. Jupiter is surrounded by a thick atmosphere primarily of hydrogen and helium that gradually becomes liquid as you move inward. The only solid matter in Jupiter is its core. No. Jupiter is surrounded by a thick atmosphere primarily of hydrogen and helium that gradually becomes liquid as you move inward. The only solid matter in Jupiter is its core.

WHAT DID YOU THINK? Is Saturn the only planet with rings? Is Saturn the only planet with rings? No. All four outer planets (Jupiter, Saturn, Uranus, and Neptune) have rings. No. All four outer planets (Jupiter, Saturn, Uranus, and Neptune) have rings.

WHAT DID YOU THINK? Are the rings of Saturn solid ribbons? Are the rings of Saturn solid ribbons? No. Saturn’s rings are all composed of thin, closely spaced ringlets consisting of particles of ice and ice-coated rocks. If they were solid ribbons, Saturn’s gravitational tidal force would tear them apart. No. Saturn’s rings are all composed of thin, closely spaced ringlets consisting of particles of ice and ice-coated rocks. If they were solid ribbons, Saturn’s gravitational tidal force would tear them apart.

Essay Questions for the Final Question 6: Describe Jupiter's atmosphere and its four largest moons. Why are they similar, and why are they different?

Essay Questions for the Final Question 7: What are the similarities and differences between Jupiter and Saturn? Describe Saturn's Rings. How did they probably arise? How do we know?

Essay Questions for the Final Question 8: What are the properties shared by Uranus and Neptune? How are they unique? What is Pluto like? How about the other small bodies in the outer solar system?